This invention relates to the use of a natural gum for the emulsification of alkenyl succinic anhydrides (ASA) sizing agents in the manufacture of paper products. The natural gum may be nonionic, cationic, anionic, amphoteric, oxidized, derivatized, or otherwise modified.
Alkenyl succinic anhydrides (ASA) useful in the sizing of cellulosic materials have gained considerable commercial success. These materials were first fully disclosed in U.S. Pat. No. 3,102,064 which is hereinafter incorporated by reference. This patent discloses a certain class of chemical materials generally having the structural formula: 
wherein R represents a dimethylene or trimethylene radical, and wherein R1 is a hydrophobic group containing more than 5 carbon atoms which may be selected from the group consisting of alkyl, alkenyl, aralkyl or aralkenyl groups.
In describing the use of the ASA sizes disclosed in this reference, the patentee indicates that for effective utilization, the sizing agents must be used in conjunction with a material which is either cationic in nature or is, on the other hand, capable of ionizing or disassociating in such a manner to produce one or more cations or other positively charged groups. The cationic agents as they are defined in this reference are disclosed as xe2x80x9calum, aluminum chloride, long chain fatty amines, sodium aluminate, polyacrylamide, chromic sulfate, animal glue, cationic thermosetting resins and polyamide polymersxe2x80x9d. The patentee particularly points out as preferred cationic agents various cationic starch derivatives including primary, secondary, tertiary, or quaternary amine starch derivatives and other cationic nitrogen substituted starch derivatives, as well as cationic sulfonium and phosphonium starch derivatives. Such derivatives, as stated by the patentee, may be prepared from all types of starches including corn, tapioca, potato, etc.
With the growing commercial use of sizes of the type above described, serious problems have remained in the application of the sizes to paper stock or pulp prior to its formation into sheet or other useful forms. Part of the problem has been that the ASA sizing materials are not water soluble, and must, accordingly, be emulsified prior to application. This allows the water insoluble size to be dispersed in the pulp, thus distributed more evenly along the cellulosic fibers, and thus creating the desired effect on the final product.
Another problem is that the use of cationic starches and/or other high molecular weight cationic polymers cause the formation of machine deposits and accompanying runnability problems in the form of press picking, felt filling, and poor cylinder vat consistency control.
While the cationic agents disclosed in U.S. Pat. No. 3,102,064 have met with some success, there has been a need within the paper industry to produce a more effective xe2x80x9cemulsifying agentxe2x80x9d for ASA sizes to avoid the deposit problems and felt filling problems mentioned above. In addition, such an emulsifying agent would preferably aid in the retention of the size on the fiber, and would increase, where desired, the wet and/or dry strength of the final sheet material.
U.S. Pat. No. 4,657,946 attempts to overcome some of the disadvantages of U.S. Pat. No. 3,102,064. This reference, U.S. Pat. No. 4,657,946, discloses the use of a cationically charged water soluble vinyl addition polymer with a surfactant for providing emulsification of alkenyl succinic anhydride sizing agents. The ASA formulation of this reference comprises a cationic water soluble vinyl addition polymer, ASA, a surfactant, and water. The ASA size formulation of this reference is said to obtain superior sizing results and retention results while minimizing or eliminating paper machine deposits, felt filling, and press picking.
While this ASA size formulation of U.S. Pat. No. 4,657,946 has met with some success, particularly with regard to superior ink holdout properties of the paper products, there is still a need within the paper industry to provide a more effective ASA size formulation where the emulsion is more stable when compared to the ASA size formulation of the prior art. U.S. Pat. No. 4,657,946 also requires a high ratio of vinyl addition polymer to ASA size for effective emulsification. A more efficient and cost effective emulsifying agent is desired by the industry.
Now in accordance with an embodiment of the present invention, an ASA size formulation for an emulsion for a paper product is provided which consists of water, alkenyl succinic anhydride JASA), a natural gum, and optionally, a surfactant. The natural gum may be a nonionic gum, a cationic gum, an anionic gum, an amphoteric gum, an oxidized gum, a derivatized gum or otherwise modified gum. Preferably, in an embodiment of the invention, the natural gum comprises a natural or derivatized guar gum. The minimum molecular weight for a guar gum used in the invention may be greater than 5,000 amu, and perhaps, greater than 50,000 amu. The upper molecular weight for the natural gum used in the invention generally will be constrained by its natural composition. It is not the intention of the inventors to restrict the invention based on molecular weight.
The ratio of the natural gum to the ASA can range from about 0.01:1 to about 100:1, and preferably this ratio range is from about 0.01:1 to about 20:1.
It is accordingly an object of the invention to provide an improved ASA size emulsion comprising water, alkenyl succinic anhydride (ASA), optionally a surfactant, and a natural gum, whereby the natural gum is such that it enhances the performance of the ASA by one or all of the following mechanisms: 1) increasing the retention of the size by the fiber; 2) creating a more even film to be distributed on the fiber; 3) decreasing deposits; and 4) improving the physical and chemical stability of ASA size formulation when stored and/or prior to the ASA size formulation being fed to the stock slurry. The improved ASA emulsion is also more hydrolytically stable than the ASA emulsions of the prior art.
Physical stability of the ASA emulsion is aided by small emulsion droplets that are stabilized or hindered from coalescence. Larger, and therefore fewer, particles do not spread as evenly along the cellulose fibers. Chemical stability generally refers to the resistance of the emulsified ASA to hydrolysis of the anhydride to acid form. The hydrolysis product of ASA is considered, in general, not to be an effective sizing agent.
A further object of the invention is the use of a natural gum as an additive and an emulsifying agent for ASA size for a paper product, i.e., paper and paper board thereby stabilizing the emulsified mixture so that the mixture may be stored for long periods of time prior to the emulsified mixture being fed into a pulp slurry in a paper machine during a paper making process. The improved ASA size emulsion, preferably, is very stable and more resistant to hydrolysis of the ASA size compared to the ASA size emulsions of the prior art.
In addition to a natural gum, the invention provides for the addition of a surfactant or other emulsifying agent to the ASA size formulation to further enhance the effect of the natural gum in the ASA size emulsion, and thus, the effect of the ASA size emulsion in the paper product.